Conventionally, a throw-away cutting tool with a cutting insert attached to a holder is used for a cutting tool for use in cutting process. Such a cutting insert used for this cutting tool is generally configured to include an upper surface, a lower surface and a side surface, and a cutting edge is formed at an intersecting portion between the upper surface and the side surface. By bringing the cutting edge into contact with a workpiece such as a metal member, it is possible to cut a workpiece.
A configuration of such a cutting tool is proposed in which projections (breaker projections) to be in contact with chips of workpieces are provided on an upper surface thereof in the same manner as the cutting insert disclosed in Patent Document 1. The cutting insert disclosed in Patent Document 1 curves a chip of a workpiece into a spring shape by bringing the chip into contact with a breaker projection, and cuts the chip by a bending stress applied to the chip upon curving.
Further, the cutting insert disclosed in Patent Document 1 has two breaker surfaces to support a difference in a chip width upon small depth cut and large depth cut. Consequently, it is possible to provide a cutting insert of a wide range of cutting process.
In recent years, a cutting insert which performs good chip processing under a wider range of cutting conditions is demanded. However, the cutting insert disclosed in Patent Document 1 has difficulty in performing a wide range of cutting process. This is because the cutting insert disclosed in Patent Document 1 has projections of oval spherical shapes, and chips are placed in point contact with the projections. When projections have oval spherical shapes, a chip is curved at an adequate position of a curved surface and angle according to a fine change in the feeding amount upon low feed process. However, when the feeding amount is great and a cutting amount is also great, a chip can easily get over the projection of the oval spherical shape. Therefore, even when two projections of spherical surface shapes are provided according to a feeding amount, and when the feeding amount is great and the cutting amount is great, there is a problem that a chip gets over a projection, is stretched long, and then damages a machined surface or entangles with a tool holder.
Patent Document 1: Japanese Patent Laid-Open Publication No. 8-11008